Many circuits require an accurate reference clock signal. One popular circuit for providing such a clock signal is the Pierce oscillator, which is shown in FIG. 1. Referring to FIG. 1, the Pierce oscillator includes an amplifier 102 and a crystal 104 connected in parallel, with each side connected to ground by a respective load capacitor C. The output of amplifier 102 provides a clock signal 106. The Pierce oscillator is often implemented within the integrated circuit to be clocked, with the exception of crystal 104, which is implemented externally.
With the increasing prevalence of mobile devices, power consumption has become a major concern. Many integrated circuits for such mobile devices now feature a low-power mode in which the power consumption of the integrated circuit is greatly reduced. Conventional integrated circuits having such a low-power mode generally disconnect the internal Pierce oscillator to save power, and instead rely on an external clock circuit while in low-power mode.